How does brake pad warning light work?
 

Hey,

I've just come out from working on a local companies computers to find on driving, when the brake is slightly applied, the brake pad wear light flickers as the wheel goes round (only seems to come on at one place in the wheels rotation at the moment). To see if it's front or rear, I tried pulling the handbrake while driving - no light. This implies it's front brakes, but I only changed the front pads around 6,000 miles ago, how long should they last??

As I remember from when I installed them, they'll only warn of wear on the pads, not the discs, is that true?

Is the light supposed to come on only when applying the brake, or does it stay lit permanently?


thanks

Russ!

Simple little lamp circuit where the sensor [ basically, just a wire]
is embedded into the pad to a certain depth. When the pad wears down to that thickness, the wire grounds out aginst the rotor and completes the lamp circuit..... usually when applying the brakes , but sometimes when just turning/rolling , etc....

If the front pads were replaced recently as you state, the rear brake pads could still be causing the light to come on. The application of the parking brake applies a different brake system than the normal service brakes. The parking brakes are a set of brake shoes (not pads) which utilize the center section of the rear rotors as it's drum.
I am not sure if your car has rear sensors though, they do vary a little from model to model.
It is fairly normal for the brake pad warning to flicker on and off, mostly coming on when the brake pedal is depressed.
Another possiblity is that when the front pads were replaced that the sensors were improperly installed.

Gilly

My brake indicator bulb flickered on my W124 when the brakes wore down on the front, as if there was a slight amount of disc warpage...went away with new front pads...I don't think my rear pads were equipped with sensors though...

PS
As GB says, some models have rear pad wear sensors-- these would be models with ASR option..
Reasoning for them on ASR is that traction is controlled via braking of the spining wheel...

The lamp indicates nothing about rotor wear/condition

Arthur:
As a general rule I would say you are correct; if an MB has ASR it will have rear sensors. But just when you think you have it figured out, you'll see a non-ASR car that also has it. Very strange.

Gilly

That's good to know.
Whenever I see a lamp , I pull a rear wheel anyway..if for no other reason but to check the rear pads, but due to my limited brake work, I have only noticed rear sens w/ASR..
Thanks for the tip...